Conventionally, a portable device, such as a vehicle navigation device, a cellular phone and a smart phone, is equipped with a position detection device including a GPS (Global Positioning System) receiver, receives signals from GPS satellites orbiting the earth, detects a current position, and outputs it on a screen or other.
However, when a vehicle or a person with the portable device goes through urban areas or mountainous regions, electromagnetic waves emitted from GPS satellites arrive at the GPS receiver via various paths since the electromagnetic waves are affected by shielding, reflection, diffraction, dispersion or others due to structures such as tall buildings, trees, geographical features, etc. Thus, in urban areas or mountainous regions, the position detection device is not able to output any current position precisely since the GPS receiver is subject to multipath effect.
Then, it has been proposed to compensate the multipath effect in order to supply position detection devices, which are able to output current positions precisely (For example, refer to Patent Documents 1 and 2).